Disadvantaged inner-city African American communities have disproportionately high rates of substance abuse and HIV/AIDS. Among those HIV seropositive, African Americans and substance abusers tend to have suboptimal medical service use and medication adherence and more rapid illness progression. Optimal use of HAART requires near complete adherence for an indefinite period of time, necessitating behavioral interventions with long-term sustainability. Social support has consistently been found to be associated with HIV medication adherence, health service utilization, and other health-related behaviors. Literature on informal caregiving suggests that main supportive ties of the chronically ill may be important targets of medical adherence intervention. The goals of the proposed study are to examine the role of main supportive ties among injection drug users (IDUs) in promoting and impeding HIV medical service utilization and HAART adherence, and to develop, pilot, and manualize a culturally appropriate adherence promotion intervention based on these findings. The proposed study builds on our research team's extensive prior research on IDUs'informal HIV caregiving, social networks, HIV adherence, and successful prevention intervention research, medical adherence in vulnerable populations. Most care for the chronically ill is provided informally by family and friends. Among the chronically ill, receipt of instrumental assistance, as informal care is operationalized, is associated with better medical adherence. Low income African Americans compared to higher income whites provide more informal (HIV) caregiving and report lower caregiving-related distress, yet are more likely to cease informal caregiving. Findings have demonstrated that African American IDUs'main supportive ties are not only important sources of support but may influence their health-related behaviors. The proposed study is based on theories of social influence and network resource exchange and utilizes an innovative social network approach to the examination of social environmental influences on adherence behaviors. As antiviral therapies rapidly begin to become part of HIV programs in developing countries over the next few years, network approaches may be viable options for effective, low cost, community-based adherence promotion in low resource settings. Four years funding is requested for four semi-annual assessments of a community sample of 500 former IDUs living with HIV/AIDS and up to two of their main HIV-related supporters (n=400). Assessments will include viral load and CD4 count, and for a subset, MEMS caps, computerized clinical, and medical service use records for validation of self-reports. Study findings will contribute to the identification of appropriate targets and approaches for the behavioral adherence intervention.